Method for producing titanium dioxide pigment

ABSTRACT

THE PRESENT APPLICATION IS A DIVISION OF APPLICATION SER. NO. 723,70, FILED APR. 24, 1968, AND RELATES TO A NOVEL METHOD FOR PRODUCING A RUTILE TIO2 PIGMENT BY A VAPOR PHASE PROCESS WHEREIN THE HEAT REQUIRED FOR THE REACTION OF THE GASEOUS TICL4 WITH OXYGEN IS PROVIDED BY A COLUMN OF HOT COMBUSTION GASES WHICH FILLS THE ENTIRE CROSSSECTION OF A PRE-COMBUSTION CHAMBER IMMEDIATELY PRECEDING A FEEDING RING DESIGNED TO INTRODUCE GASEOUS TICL4 INTO THE COLUMN OF HOT GASES FROM A MULTIPLICITY OF RADIAL APERTURES SURROUNDING THE COLUMN OF HOT COMBUSTION GASES AND LYING IN A COMMON PLANE SUBSTANTIALLY AT RIGHT ANGLES TO ITS LONGITUDINAL AXIS, THE REACTION THE TICL4 WITH THE O2 IN SAID HOT GASES TAKING PLACE WITHIN A RELATIVELY SHORT REACTION ZONE IMMEDIATELY SUCCEEDING THE TICL4 FEEDING RING THUS INSURING HIGH REACTION TEMPERATURES, SHORT REACTION TIME, UNIFORM RESIDENCE TIME AND NO REVERSE CURENTS IN THE REACTION ZONE.

A. KULLING ETAL 3,582,278

2 Sheets-Sheet 1 June 1,1971

I METHOD FOR PRODUCING TITANIUM DIOXIDE PIGMENT Originl Filed April 24,1968 0 4 0 Fv 2 "v I M ZZZM/ o 5 U r 8 d o \v w D \H' M II Z/ZMM/Z v WWm w W &

INVENTORS Achim Kullinq Hons Stainboch Hermann Trueb AGENT Fig. 3.

June 1,1971 KULLING ETAL 3,582,278

METHOD FOR PRODUCING TITANIUM DIOXIDE PIGMENT Original Filed April 24,1968 2 Sheets-Sheet I [III II I 'l/ I III/fl] 45 r co /7\ 11 l W3? 6 f4;

INVENTORS Achim Kullinq nuns Steigboch 47 37 ermann rueb AGENT UnitedStates Patent Oihce 3,582,278 Patented June 1, 1971 Int. Cl. c1 23/04US. Cl. 23-202 Claims ABSTRACT OF THE DISCLOSURE The present applicationis a division of application Ser. No. 723,700, filed Apr. 24, 1968, andrelates to a novel method for producing a rutile TiO pigment by 'a vaporphase process wherein the heat required for the reaction of the gaseousTiCl with oxygen is provided by a column of hot combustion gases whichfills the entire crosssection of a pre-combustion chamber immediatelypreceding a feeding ring designed to introduce gaseous TiCL; into thecolumn of hot gases from a multiplicity of radial apertures surroundingthe column of hot combustion gases and lying in 'a common planesubstantially at right angles to its longitudinal axis, the reaction ofthe TiCl, with the O in said hot gases taking place within a relativelyshort reaction zone immediately succeeding the TiC1 feeding ring thusinsuring high reaction temperatures, short reaction time, uniformresidence time and no reverse currents in the reaction zone.

BACKGROUND OF THE INVENTION The invention is concerned, in general, witha process for the manufacture of a rutile pigment by reaction oftitanium tetrachloride with oxygen in the presence of hot combustiongases produced by combustion of carbon monoxide with oxygen the hotgases being brought into contact with the gaseous titanium tetrachlorideand, as the case may be, with further oxygen, and mixed thoroughlywhereby a reaction takes place with the formation of titanium dioxide.The reaction product gases containing the titanium dioxide produced bythe reaction are subsequently cooled, whereupon the titanium dioxide isseparated from these gases.

For the manufacture of a good rutile pigment it is neces sary that thereacting gases be mixed thoroughly and rapidly and that the reactiontake place at high temperatures. The procedure is, in general, such thatthe titanium dioxide formed is maintained initially at elevatedtemperature for sufficient time to achieve a transformation of thetitanium dioxide from the anatase form first produced to the rutileform. However the residence time of the pigment in the zone of hightemperature must not be too long because otherwise a particle sizeincrease occurs which causes an impairment in pigment qualities. Also inorder to promote rutile formation and/or obtain additional goodpigmentary properties it is often the practice to add slight amounts ofother substances e.g. water, aluminum trichloride, silicontetrachloride, zirconium tetrachloride, etc. to the reactants.

Furthermore, special precautions must be observed during the reaction inorder to reduce formation of titanium dioxide deposits at the mouths ofthe gas inlet pipes and on the chamber walls; and any such deposits soformed must be removed since such deposits disturb the reaction andreduce the quality of the products obtained.

British patent application No. 1,010,061 describes a process in whichthe hot combustion gases produced by the combustion of carbon monoxideand oxygen, comprises a thin stream which is blown in centrally into arelatively wide reaction chamber, wherein shortly before entering thereaction chamber gaseous titanium tetrachloride is added to the hot gasmixture through separate supply pipes. Also a laminar current of gas isconducted along the chamber walls toward the exit of the chamber for itsprotection. This gas consists of a part of reaction product gas that hasbeen produced in the reaction, freed of its titanium dioxide burden andpreferably cooled.

In another process (Dutch patent application No. 298,- 87 2) carbonmonoxide is burned in a precombustion chamber with oxygen to form hotcombustion gases which are introduced into a relatively Wide reactionchamber through a narrow pipe wherein at the point of introduction intothe wide reaction chamber gaseous titanium tetrachloride is introducedtogether with a current of chlorine which is passed between the hotgases and the gaseous TiCl Below the place where the reaction proper oftitanium tetrachloride with oxygen begins, a cold inert gas may beintroduced into the reaction chamber in order to cool down the reactionproducts stepwise.

According to the process described in the British patent application1,047,713 oxygen is reacted with carbon monoxide in a pre-combustionchamber and the hot gas mixture produced thereby is conducted through aconstriction into a relatively wide or widening reaction zone therein.Shortly after entering the reaction zone, a mixture of titaniumtetrachloride and excess oxygen is introduced into the hot gas mixture.

Furthermore, a process has become known (South African patentapplication No. 2,153/66) in which hot gases formed by the combustion ofa carbon compound in a pre-combustion chamber are introduced axiallyinto a reaction chamber conically widened toward its outlet, whiletitanium tetrachloride is introduced into the reaction chamber via inletpipes in the side thereof, wherein a cold inert gas may be introducedtangentially below the titanium tetrachloride inlet pipes for rinsingthe wall of the chamber.

However all known processes have the disadvantage that the reaction ofthe titanium tetrachloride and oxygen takes place in a relatively longreaction chamber and moreover the reaction fills only a part of thereaction chamber cross-section, the effect of which is to producereverse gas currents therein. Consequently the residence times of theindividual titanium dioxide particles in the reaction chamber differgreatly; when the residence times are too short the conversion to rutilewill not have been completed and the particle size is possibly too fine;while if the residence time is too long the product is overcalcined andits particle size is too coarse. Thus, the product is non-uniform anddoes not measure up to the high requirements which are demanded for ahigh quality rutile pigment in many fields of application.

Further, owing to the great length of these reaction chambers or theunsuitable shape of these chambers, considerable effort is required inorder to keep the chamber walls free of deposits. The methods suggestedfor this purpose, in the' processes of the prior art, are frequentlyunsatisfactory. The gas which is used in some cases as a protective filmon the chamber wall is prone to mix easily with the reacting gases owingto unfavorable flow conditions and hence protection of the wall isunsatisfactory and impairment of the reaction occurs. Also the use of afinely divided inert solid substance to keep the reaction chamber wallfree of deposits, for example, as described in the South Africanapplication No. 2,153/66, is unsatisfactory since, following thereaction, the solid inert material must be separated and removed fromthe titanium dioxide.

SUMMARY OF THE INVENTION The present invention overcomes thedisadvantages attending the methods of the prior art. In general apyrogenic rutile titanium dioxide pigment is produced by the reaction ofgaseous TiCl with the oxygen in a column of hot combustion gasesproduced by separate combustion of carbon monoxide and an excess ofoxygen or a gas containing oxygen, the gaseous TiCL; being introducedinto the column of hot combustion gases from a ring of radial jets in acommon plane at substantially right angles to the longitudinal axis ofthe column of hot gases and in a manner such that the reaction takesplace in a reaction zone of relatively short length and oversubstantially the entire cross section thereof. This has beenaccomplished by designing a reactor with a cylindrical precombustionchamber, succeeded by a TiCl feeding ring having an inner diametersubstantially equal to the inner diameter of the precombustion chamber;a relatively short cylindrical reaction chamber below the TiCl, feedingring, and a burner manifold at the entrance end of said precombustionchamber having burners designed to produce a column of hot combustiongases which, in passing from the precombustion chamber into the reactionchamber, fills the entire cross sectional area of the TiCl feeding ring;the gaseous TiCl being adapted to issue from a multiplicity of radialjet apertures in the inner wall of the TiCl feeding ring surrounding thecolumn of hot gases and to penetrate the latter in a manner such thatthe reaction of the TiCl with the oxygen in the hot combustion gasestakes place over substantially the entire cross sectional area thereof.The reaction of the TiCl and oxygen is thus initiated within the TiCL,feeding ring and, as hereinafter disclosed, is substantially completedwithin the upper portion of the reaction chamber. The space between thefeeding ring and the upper portion of the reaction chamber beingreferred to hereinafter as the reaction zone.

In this connection the exit velocity of the radial TiCl jets is selectedon the bases of the cross-sectional area of the reaction zone, asmeasured by the inner diameter of the TiCl feeding ring, and thevelocity of the hot combustion gases such that the TiCld, jets penetratethe column of hot gases far enough to maintain the reaction over theentire area of the TiCl feeding ring but not so far as to strike theopposite walls thereof. To meet these conditions the throughput ofgaseous TiCl has been determined to be from 5000 to 40,000 kg./hr. persq. m. of reaction zone cross section. The invention also features theuse of two rinsing gas feeding rings, one assembled between the exit endof a precombustion chamber and the TiCL, feeding ring, and the otherbetween the latter and the entrance end of a reaction chamber. Theformer rinsing gas feeding ring has an inner diameter equal to the innerdiameter of the precombustion chamber While the latter feeding ring hasan inner diameter equal to that of the reaction chamber, the innerdiameter of which is slightly larger than that of the TiCL; feeding ringand precombustion chamber.

The first rinsing gas feeding ring is adapted to provide a protectivelayer of cool gas at the TiCL; jet apertures to prevent Ti fromdepositing thereon; and to counteract any counterflow of the reactantgases into the precombustion chamber. The second rinsing gas feedingring is adapted to provide a film of cool gas on the wall of thereaction chamber to protect it from the hot gases and to preventdeposits of TiO from forming thereon.

With a reactor of this design and operated as described above thereaction of the gaseous TiCl with the oxygen in the column of hotcombustion gases is made to take place over the entire area of thereaction zone which is relatively short in length as a consequence ofwhich the temperature in the reaction zone is uniformly high, the

gaseous TiCl, is reacted in a relatively short time, the residence timeof the TiO particles in the reaction zone is uniform and there is noreverse currents or Ti0 deposits to interfere with the reaction.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical elevation in section ofthe reactor of this invention comprising, in integral superposedrelationship, a burner manifold, a precombustion chamber, an upper gasfeeding ring, a TiCl, feeding ring, a lower gas feeding ring and areaction chamber;

FIG. 2 is an enlarged plan view of the TiCl feeding ring of FIG. 1;

FIG. 3 is an elevation in section of the TiCl feeding ring on line 33 ofFIG. 2;

FIG. 4 is an enlarged fragmentary elevation in section of theprecombustion chamber showing a modified form of burner manifoldsuperposed thereon;

FIG. 5 is an elevation in section of a modification form of burnermanifold used with the reactor of this invention; and

FIG. 6 is a plan view in section of the modified burner manifold of FIG.5 on line 6-6 showing details of the individual burners.

DESCRIPTION OF PREFERRED EMBODIMENT Before describing the structuraldetails of the reactor shown in the drawings it should be emphasizedthat in its preferred embodiment the process of the invention ischaracterized in that the column of hot combustion gases in thecylindrical precombustion chamber is produced with the aid of a burnermanifold having multiple burners which provide uniform admission of thehot reacting gases into the precombustion chamber where the reaction ofthe gases is completed, the resulting hot combustion gases filling theentire cross section of the precombustion chamber and forming, ineffect, a solid column of hot combustion gases which passes through theTiCl feed ring into the cylindrical reaction chamber arranged in axialalignment therewith. The unmixed gaseous titanium tetrachloride is blowninto the column of hot combustion gases radially from a plurality of jetapertures located in a common plane at right angles to the longitudinalaxis of the column of hot gases and distributed around the entirecircumference thereof wherein the throughput of titanium tetrachloridedivided by the cross-section of the reaction zone is from 5000 to 40,000kg./hr./sq. In. Directly above and below the titanium tetrachloride jetopenings rinsing gases are introduced tangentially into theprecombustion chamber and reaction zone by means of upper and lower gasfeeding rings respectively. In this connection the inner diameter ofthat portion of the reaction zone defined by the lower rinsing gasfeeding ring and the upper portion of the reaction chamber is slightlylarger than the inner diameter of the TiCL, feeding ring so as toprovide an annular step or shoulder as and for the purpose hereinafterdescribed.

According to the process of the invention the production of the columnof hot combustion gases and the reaction of the gaseous titaniumtetrachloride therewith are carried out spatially separately andconsecutively in a cylindrical space of practically constant diameterwith smooth walls and without built-in parts. Using this geometricconstruction combined with a high throughput of gaseous TiCl per unit ofcross-sectional area, the conditions for clean-cut flow withoutback-currents are met. The hot combustion gases are the product of anauxiliary flame produced by combustion of CO and O in the burners of theburner manifold and fill the entire cross-section of the precombustionchamber uniformly, the column of hot gases being pushed downwardly bythe succeeding gases and having, at all points of its cross-sectionessentially the same velocity and temperature. The gaseous titaniumtetrachloride is divided into many small jets and blown radially intothe column of hot gases. By this means a fine and intensive distributionof the titanium tetrachloride in the hot combustion gases is achieved inconsequence of which the reaction takes place uniformly oversubstantially the entire cross-section of the reaction zone and extendslongitudinally only a relatively short distance. This reaction zone isvery hot so that the titanium tetrachloride is reacted in a very shorttime. Moreover while some minute gas turbulence may be present noreverse gas currents appear. The residence time of the individualtitanium dioxide particles in the reaction zone is thus of uniformduration and for that reason a uniform pigment particle size with goodproperties is obtained.

A decisive advantage of the process according to the in vention is thefact that the reaction occurs fast and over a short distance. Themaintenance of uniform temperature and retention times for all titaniumdioxide particles is strongly favored thereby. In addition, a relativelyshort reaction zone results which facilitates freeing the chamber wallfrom deposits and only a small amount of rinsing gas is needed for thispurpose. It is possible at a throughput of 500 kg./ hr. titaniumtetrachloride to achieve complete reaction in a reaction zone of from150to 200' mm. length.

The length of the reaction zone and the duration of the reaction andtherefore, uniformity of pigment particles size depend essentially onthe rapid and uniform mixing of the-titaium tetrachloride with theoxygen in the column of hot combustion gases over the entirecross-section of the reaction zone. For this purpose the sub-division ofthe gaseous titanium tetrachloride into a fairly large number oftitanium tetrachloride jets is necessary since the subdivision into afew jets only results in non-uniform mixing. To this end thecross-section and the exit velocity of each individual titaniumtetrachloride jet must be adjusted to the cross-section of the reactionzone and the velocity of the hot combustion gases in such a way that thetitanium tetrachloride jets penetrate the column of hot gasessufficiently but not too much. If they penetrate the hot combustiongases too little a relatively long mixing zone results and a non-uniformmixing occurs. If they penetrate too far, pigment deposits are formed onthe opposite wall of the TiCL, feeding ring portion of the reactionzone. In order to meet this condition the titanium tetrachloridethroughput divided by the reaction zone cross-section should amount to5000 to 40,000 kg./hr./ sq. m. In this connection it is alsoadvantageous to inject the gaseous titanium tetrachloride in at aninitial impulse -per titanium tetrachloride jet divided by the reactionchamber diameter of 0.02-6 kg./m.

Concerning the hot combustion gases in the precombustion chamber, thesegases should have a certain fine turbulence without that regressivecurrents occur, and in addition, the temperature as well as velocity ofthe gas mixture should be as uniform as possible over the entirecross-section of the precombustion chamber. For these purposes it isexpedient to divide the oxygen or the gas containing oxygen and thecarbon monoxide, either mixed or separated, into separate streams andfeed them to a plurality of individual burners of a burner manifoldsuperposed on said precombustion chamber, the individual burners being,if desired, regulated separately for the control of the gas flow. Forexample, the individual burners may be charged at different rates. Itmay also be of advantage to give both gases, in each individual burner,a counter-current spin which may be accomplished by suitable inserts.Further in order to maintain the desired velocity and temperaturedistribution of the hot gases up to the point where it is reacted withthe titanium tetra chloride, it is advantageous not to have theprecombustion chamber too long and to have it insulated against heatlosses, as the case may be.

The length of the reaction zone as defined by the distance between theTiCl feeding ring and the upper portion of the reaction chamber may bevaried within certain limits, whereby the pigment characteristics aremodified. With a short reaction zone the pigments obtained are of fineparticle size; while with longer reaction zones the pigment particlesare coarser. Good pigments are obtained when the length of the reactionzone is 0.5-3 times its diameter.

A further advantage of the invention is seen in the fact that a rutilepigment is obtained, a pigment which along with other good propertiesdoes not contain any detectable amounts of anatase, i.e. less than 0.3%anatase. On the other hand, if a small amount of anatase is nottroublesome, lesser amounts of addition agents will be required whichleads, among other things, to savings in aluminum trichloride.

The rinsing gas of the upper rinsing gas feed ring fulfills twoessential functions namely, it forms a protective gas layer at the jetapertures of the titanium tetrachloride feeding ring so that no TiOdeposits can be formed there. Also it counteracts any counter-flow ofthe TiO and TiCL, burdened reacting gases back up into the precombustionchamber. In this connection the impulse of the upper rinsing gas must beadjusted to the impulse of the jet streams of titanium tetrachloride. Ifthe impulse of the rinsing gas is too low, then titanium dioxidedeposits may be formed at the lower end of the precombustion chamberwhereby the reaction is badly hampered. On the other hand if the impulseof the rinsing gas is too strong, then the titanium tetrachloridestreams that normally must penetrate the rinsing gas film in order tocome into contact with the column of hot gases are carried along by therinsing gas film and the reaction will be incomplete.

The rinsing gas of the lower rinsing gas feeding ring also has twofunctions namely, it protects the wall of the reaction zone against thehot reacting gases; and prevents the formation of titanium dioxidedeposits on the walls of the reaction zone. It is essential that thisrinsing gas form a stable gas film or layer on these walls that does notmix to any extent with the reacting gases. For this reason the rinsinggas must be introduced under very definite flow conditions. It must havea certain minimum linear velocity at the inlets, and the rinsing gasthroughput per sq. m. of wall surface must not fall below a certainfigure; the same is true for the product of introductory velocity andthe rinsing gas throughput per sq. In. of coated wall surface.Furthermore, the rinsing gas must have a considerably lower temperaturethan the reacting gases. In order to support the effect of the rinsinggas film the walls of the reaction zone and reaction chamber may becooled additionally from the outside. The conditions mentioned above areexplained in more detail in the German patent application T-29994 IVa/12 n-T-650, and corresponding to US. application Ser. No. 585,064 filedOct. 7, 1966.

It is also important to the production of a high quality rutile pigmentthat the portion of the reaction zone directly below the titaniumtetrachloride feeding ring has a slightly larger inner diameter than theinner diameter of the TiCl; feeding ring so as to form an annular lip orstep. This step permits the lower rinsing gas film to flow downwardlyonly. In general, the width of the annular step is ca. 1-2 cm.

The titanium tetrachloride jet inlets are designed in such a way thatthe gaseous titanium tetrachloride will enter into the column of hotcombustion gases radially and in a common plane substantially at rightangles to the longitudinal axis of the pre-combustion chamberalthoughslight deviations from this angle are possible. The size of thecross-section of the individual jet inlets depends on the titaniumtetrachloride throughput, the number of jet inlets and the impulse withwhich the titanium tetrachloride jets enter the reaction zone. Also thejet inlets may be of different shape in cross section for example,circular, rectangular or slot-like for it has been found that the shapeof the inlets exert a certain influence on the mixing of the titaniumtetrachloride with the hot combustion gases. Moreover thecross-sectional area of the individual titanium tetrachloride jet inletsshould not be smaller, in general, than 3 sq. mm. since otherwiseclogging may occur; and the inlets may all have the same crosssection.However when using a reaction zone of relative large diameter it isadvantageous to use jet inlets of varying shape and/or size. By thisexpedient the individual titanium tetrachloride vapor jets are projectedat various distances into the column of hot gases whereby a particularlygood and uniform mixing of the titanium tetrachloride with the hot gasestakes place over the entire reaction zone cross-section.

It is generally favorable to use oxygen in excess of the amountnecessary for the combustion of the carbon monoxide as well as for thereaction of the titanium tetrachloride; and the temperature of the hotcombustion gases may be above 2000 C. Also the titanium tetrachloride isintroduced in gaseous form and to this end preheating of the titaniumtetrachloride above its boiling point is possible.

Although it is preferable to add all of the excess oxygen with thecarbon monoxide through the multiple burner arrangement it is sometimesadvantageous to introduce a part of the oxygen necessary for thetitanium tetrachloride reaction into the precombustion chamber with theupper rinsing gas. In this case a higher temperature is reached in thehot gas mixture; besides that, a smaller amount of inert gas is requiredfor the upper rinsing gas. However when adding oxygen to the upperrinsing gas, it must be kept at a very low temperature when entering thechamber, preferably room temperature for otherwise, a premature reactionbetween rinsing gas and titanium tetrachloride may take place and TiOdeposits formed on the chamber wall.

As rinsing gases the same gas or different gases may be used in both theupper and lower feeding rings. For example, nitrogen, chlorine, oxygen,air or mixtures of such gases are suitable. Particularly suitable in areaction product gas cooled and free from titanium dioxide.

It is often expedient to cool the TiCl, inlet apertures, the rinsing gasapertures and the multiple burner apertures of the burner manifold. Thecooling may be done by a gas or a liquid.

Referring now to the drawings: FIG. 1 shows in cross- 'section, areactor for carrying out the process according to the invention. The topof the reactor comprises a burner manifold characterized by a plenumchamber 1 having multiple flame apertures or burners. To the burnermanifold are attached, in succession, a cylindrical precombustionchamber 2, an upper feeding ring 3 for the introduction of a rinsing gasinto the precombustion chamber and a ring 4 for the introduction ofgaseous titanium tetrachloride into the reaction zone delineated byarrows 8, the inner diameters of the precombustion chamber and the TiClfeeding ring being equal. Another feeding ring is indicated at 5 for theintroduction of a rinsing gas into the reaction chamber 6. Both therinsing gas feeding ring 5 and the reaction chamber 6 are of equal innerdiameter which is slightly greater than that of the TiCl feeding ring 4so as to form an annular step 7. At the lower end of the reactionchamber 6 is a discharge opening 9. The precombustion chamber 2 isprovided with insulation 10. The feeding rings 3 and 5 for rinsing gaseach have a ring-shaped channel 11 and 12 respectively. From thechannels 11 and 12 the rinsing gas is projected via tangential boreholes 15 and 16 into the precombustion chamber and reaction zonerespectively. Furthermore, each feeding ring is provided with coolingmeans 17 and 18 respectively.

The feeding ring 4 for the gaseous titanium tetrachloride has aring-shaped channel 19 into which gaseous titanium tetrachloride isintroduced via inlet 20. A multiplicity of radial jet apertures 21 serveto emit jet streams of the gaseous TiCl into the upper end of thereaction zone. Furthermore, the TiCL, feed ring 4 is provided withcooling means 22. The reaction chamber 6 is jacketed as indicated at 23for exterior cooling.

Referring more especially to FIGS. 2 and 3 the TiCl, feeding ring hastwo concentric channels 19 and 24. The outer channel 19 has an inlet 20for gaseous titanium tetrachloride and a multiplicity of radial jetapertures or inlets 21 in its inner wall for emitting streams of gaseousTiCl, into the center 25 of the reaction zone. The inner channel 24 isdisposed in a plane below the jet inlets 21 and serves for circulating acoolant through the feeding ring, the pipes 26 and 27 serving for theintroduction and discharge of the coolant.

In the feeding ring shown in FIGS. 2 and 3 the cross-section of the jetapertures 21 may be of different size and/or dilferent form, and in eachcase it is expedient that jet apertures with different cross-sections beadjacent.

FIG. 4 shows a modification of the burner manifold. It consists of aplenum chamber 31 one wall of which comprises a plate 29 having aplurality of holes 28 entering from the plenum chamber into theprecombustion chamber; and an inlet 30 for introducing a mixture ofcarbon monoxide and oxygen into the plenum chamber. In this respect theburner manifold is similar to that shown in FIG. 1. Referring again toFIG. 4, mounted on the upper side of the perforated plate 29 is acooling pipe 32 for cooling the apertured plate, and below the plate 29is a second thicker plate 33 having a plurality of holes 34. The holes34 are of larger diameter than the holes 28 in the plate and runcoaxially with these. Below the plate 33 is the precombustion chamber 2.The mixture of carbon monoxide and oxygen enters the duct 30 into plenumchamber 31 and flows from thence through the narrow holes 28 into thewider holes 34. The combustion of the gas mixture takes place within theWider holes 34. Thus back-firing of the flames is prevented by the factthat the gas mixture flows at high speed through the narrow and cooledholes 28.

Still another suitable type of burner manifold is shown in FIGS. 5 and6. In this type of burner manifold the carbon monoxide and oxygen areintroduced separately into a number of individual burners 35. Eachindividual burner consists of two concentrically arranged open-endedtubes 36 and 37 the tubes 36 projecting downwardly from the bottom plate39 of the plenum chamber 40 and the tubes 37 projecting upwardly fromthe plate 41 which forms the upper closure of the precombustion chamber2 and is cooled by a cooling agent flowing through a system of channels42 therein. With this arrangement each set of concentric tubes 36 and 37defines an annular slot or opening 38 communicating with the chamber 44and the precombustion chamber 2. Chamber 44 is also provided with ducts43 through which carbon monoxide passes into the chamber 44. Also eachannular slot 38 is shown provided with suitable blades 45 whereby the COgas is given a spin as it passes through the slots. The oxygen isintroduced through duct 46 of the burner manifold into its plenumchamber 40 and from thence passes through the tubes 36 into theprecombustion chamber 2. The tubes 36 are also provided with suitablebuilt-in blades 47 whereby the oxygen receives a spin which is in theopposite direction to that of the carbon monoxide. In this way anintensive mixing of the two gases takes place immediately after theirentrance into the precombustion chamber and the mixture burns to formhot combustion gases which fill the entire cross-section of theprecombustion chamber uniformly.

The individual parts of the device may consist of metal or ceramicmaterials.

The following examples explain the invention in more detail. The anatasecontent of the pigments produced was determined by X-ray. For testingthe pigment particle size the undertone in a gray paste was determinedaccording to a test method described by P. B. Mitton and A. E. Jacobsenin Official Digest July 1962, pp. 704-715. High values indicate finepigment particle size while low values indicate a coarser pigment size.

9 EXAMPLE 1 A reactor according to FIG. 1 was employed using thewater-cooled burner manifold shown in FIG. 4 having 48 burner apertures28 and 34 respectively.

The precombustion chamber 2'was lined with a refractory mass; it had alength of 100 mm. and an inner diameter of 180 mm. The feeding rings 3,4 and 5 consisted of V A stainless steel and each of rings 3 and 4 hadan inner diameter of 180, while ring 5 and reaction chamber 6.had aninner diameter of 200 mm. so that the reaction zone had an annular step7 10 mm. wide. The feeding rings 3 and 5 were cooled with water and hadfour tangential apertures 15 and four tangential apertures 16respectively each aperture having a cross-section area of 78.5 sq. mm.The reaction chamber 6 consisted of aluminum, had an inner diameter of200 mm. and was cooled with water. The reaction zone 8 had a length of150 mm.

The feeding ring 4 for the introduction of gaseous titaniumtetrachloride was constructed as shown in FIGS. 2 and 3. It was 60 mm.high and was air cooled. Forty radial disposed jet apertures 24 mm. longled from the ring channel 19 through theinner wall of the ring eachaperture having a cross-section of 36 sq. mm.

120 standard cu. m. per hr. of a carbon monoxideoxygen mixture at roomtemperature, which consisted of 33% by volume of carbon monoxide and 67%by volume of oxygen, were introduced into the plenum chamber 31 of theburner manifold and burned to produce hot combustion gases in theprecombustion chamber 2. 50 standard cu. in. per hr. of a gas mixture atroom temperature, consisting of 50% by volume of oxygen and 50% byvolume of reaction product gas divested of TiO; were introduced into theprecombustion chamber through the rinsing gas feeding ring 3. Alsothrough rinsing gas feeding ring 5 40 standard cu. m. per hr. reactionproduct gas divested of TiO and cooled to room temperature wereintroduced into the reaction Z0116. Through the jet apertures 21 offeeding ring 4 500 kg. per hr. titanium tetrachloride at a temperatureof 350.C. were injected into the reaction zone; prior to its additionaluminum trichloride in an amount of 2%, calculated as A1 and on thebasis of pigment, were added to the titanium tetrachloride.

The quotient of titanium tetrachloride throughput and reaction zonecross-section was 15,800 kg. per hr. per sq. m. and the ratio of thelength of the reaction zone to its diameter 0.75. A very good rutilepigment with an undertone value of +4.1 was obtained; no anatase couldbe detected in the pigment (limit of detection 0.2% anatase).

EXAMPLE 2 A reactor such as shown in FIG. 1 was employed, wherein aburner manifold of the type disclosed in FIGS. and 6 was used. Theburner manifold had seven individual burners 35 and was water-cooled.The precombustion chamber 2 was lined with a refractory and had a lengthof 300 mm. and an inner diameter of 180 mm.

The feeding rings 3, 4 and 5 were made of nickel, each of rings 3 and 4having an inner diameter of 180 mm. and ring 5 an inner diameter of 200mm. so that the reaction zone had an annular step 7 mm. wide. Thewater-cooled reaction chamber 6 was made of aluminum, had a length of300 mm., and inner diameter of 200 mm. and abutted the feeding ring 5.The feeding rings 3 and 5 for rinsing gas and the feed ring 4 fortitanium tetrachloride were constructed as described in Example 1. Thereaction zone 8 had a length of 350 mm.

Using this multiple burner arrangement 40' standard cu. m. per hr.carbon monoxide at room temperature and 70 standard cu. in. per hr. ofoxygen preheated to 200 C. were introduced separately into the burnermanifold and burned to produce hot combustion gases in the precombustionchamber 2. Through the feeding ring 3 60 standard cu. m. per hr. of agas mixture were introduced into the precombustion chamber at room.temperature, which mixture consisted of 50% by volume of reactionproduct gas divested of titanium dioxide and 50% by volume of oxygen.Through feeding ring 5 50 standard cu. in. per hr. reaction product gasdivested of titanium dioxide and cooled at room temperature wereintroduced into the reaction zone. 7

Through the jet apertures 21 of the TiCl feeding ring 4 500 kg. per hr.titanium tetrachloride were injected into the reaction zone as in theprevious example, at 350 C. to which 2.0% aluminumtrichloride,calculated as A1 0 on a pigment basis had been added.

The quotient of titanium tetrachloride throughput and reaction zonecross-section Was 15,800 kg. per hr. per sq. m. and the ratio of thelength of the reaction zone to its diameter was 1.75. A good rutilepigment having an undertone value of +3.0 was obtained; this time alsono anatase was detectable.

EXAMPLE 3 The same reactor as in Example 2 was employed. 40 standard cu.ml. per hr. carbon monoxide and standard cu. m. per hr. oxygen preheatedto 200 C. were introduced into the burner manifold and burned to formhot combustion gases in the precombustion chamber. 40 standard cu. m.per hr. reaction product gas freed of TiO and cooled to room temperaturewere introduced into the precombustion chamber through feeding ring 3.The addition of titanium tetrachloride through feeding ring 4 andrinsing gas through feeding ring 5 was carried out as in Example 2.

A rutile pigment identical to that in Example 2 Was obtained.

EXAMPLE 4 The same reactor as in Example 2 was employed except that thereaction zone was 550 mm. long. The process was carried out as inExample 2 with the only difference being that the volume of rinsing gasadded through the feeding ring 5 was increased to 70 standard cu. m. perhr. The quotient of titanium tetrachloride throughput and reaction zonecross-section was 15,800 kg. per hr. per sq. m. and the ratio of thelength of the reaction zone to its diameter was 2.75. A good rutilepigment with the undertone value of +1.5 was obtained; anatase was notdetectable. I

While this invention has been described and illustrated by the examplesshown, it is not intended to be strictly limited thereto, and othervariations and modifications may be employed within the scope of thefollowing claims.

We claim:

1. In a process for producing rutile TiO pigment by reacting gaseousTiCL; with oxygen in a reaction zone in the presence of hot combustiongases produced by burning CO and excess oxygen or other combustible gascontaining excess oxygen, the improvement comprising:

(a) feeding the hot combustion gases downwardly into a cylindricalprecombustion chamber in a manner to fill the entire cross-sectionalarea of said precombustion chamber and to form a column of hotcombustion gases leading into a relatively short, cylindrical reactionchamber spatially and separately positioned below said precombustionchamber;

(b) radially injecting from an annular zone, spatially and separatelypositioned below said precombustion chamber and having an inner diameterequal to the diameter of the column of hot combustion gases, gaseousTiCl into said column of hot combustion gases in the form of a pluralityof jet streams surrounding said column and lying in a plane essentiallyat right angles to the longitudinal axis thereof, the throughput of saidgaseous TiCl divided by the area of the reaction zone being in the rangeof 5000 to 40,000 kg./hr./sq. m. and the gaseous TiCl, issued from eachaperture being 0.02 to 0.6 kg. per m. of reaction zone diameter, so thatthe combustion reaction of said gaseous TiC1 with hot combustion gasestakes place immediately in the upper portion of the reaction chamber andover the entir cross-sectional area thereof;

(c) introducing through a plurality of apertures a first rinsing gastangentially, from a first annular conduit directly into saidprecombustion chamber immediately preceding the introduction of saidTiC1 jet streams, and introducing through a plurality of apertures asecond rinsing gas tangentially, from a second annular conduit, directlyinto said reaction zone immediately following the introduction of saidTiCl jet streams, respectively, the inner diameters of the reaction zoneand of the second annular conduit being equal and substantially greaterthan the diameter of the column of the hot combustion gases and theinner diameter of the first annular conduit.

2. In a process for producing a TiO pigment according to claim 1 whereinsaid rinsing gas comprises the reaction product gases produced in saidreaction zone which gases have been cooled and freed of their TiOburden.

3. In a process for producing a TiO pigment according to claim 1 whereinsaid rinsing gas comprises a mixture of oxygen or an oxygen containinggas and an inert gas. 7

4. In a process for producing a TiO pigment according to claim 1 whereinthe hot combustion gases are produced by a plurality of individualburners at the entrance end of said precombustion chamber. 7 1 1 5. In aprocess for producing a TiO pigment according to claim 4 wherein thecarbon monoxide and oxygen or oxygen containing gas are introducedseparately into each individual burner in a manner such that said gasesreceive a countercurrent spin.

References Cited UNITED STATES PATENTS EDWARD STERN, Primary ExaminerU.S. CL. X.R.

